DISK TRACK BUFFERING
Disk Track Buffering makes use of RAM on the disk drive to store data read speculatively. Older drives continue to read after a sector is read, speculating that the next sector requested will be the physical sector following the last read sector. As the price of RAM dropped, it became feasible to hold an entire track in memory on the drive. Once this became possible, disk drives simply started reading wherever they were when the track seek completes. Data is read up through the requested sectors and any following sectors that can be read while the disk is waiting for a command that will reposition the read/write heads. Potentially, an multiple tracks can be read into the disk buffer.
Reads of subsequent sectors will be supplied from the buffer rather than by reading the disk. This can greatly enhance the perceived read performance of the disk if multiple (near) contiguous sectors are read in separate operations.
Buffering can also be used for disk writing. The information is buffered in the drive waiting for head or disk motion to bring the proper place. Meanwhile, the program doing the writing is told that the operation has completed.
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Copyright 1994-2002 by Donald Kenney.